There are many ways to distinguish actually.
Websites: Never buy superbranded stuff from websites. Incase you are serious please check for the permission before buying. Ask thenm to mail you the permission copy from the respective designer. Do not be fooled. They just want to cheat your money by giving you a fine fake copy. The ONLY authorized site by Louis Vuitton is eLUXURY.com. And there is nothing called clearance sale on website. No well known brand would actually clear their stuff. Dont be gullible.
Stiches: Have a close look of the thing that you are buying. May it be bag or belt or a nice dress. Designers always inspect and test their stuff before putting them for purchase. They do a strong quality check of all their stuff. They will be absolutely flawless. Make sure that no strings have come out or some seams are missing. It does not happen actually when you buy an authentic brand.
China town: Now you know it. You are actually here becuase you want to buy fake stuff. The word "Chinatown" speaks it all and its so self explainatory. Nothing more to say.
Licensed Copies: They are NOT counterfieted items but be extra cautious while buying them. Buy them ONLY from the store. The licensing allows the brands like "Guess" to copy the Trangular lebel from "Prada". Only the word "Guess" is replaced with "Prada". Another example is "Guess" copying the "C" design of "Coach". They just replace it with a twist of G. Its difficult to distinguish a fine copy but if you are a regular buyer and have an eye for original stuff you will easily be able to figure it out.
Huge discounts: Please be aware that there is nothing wholesale or huge discounts thrown at your designer's store. Gucci or Prada will never be on huge sale like 50%. Loius vuitton is out of question. They have their own clientele and quality which doesnt bend them to go for sale.
I myself spotted good fakes at the bylanes of Karol bagh, Malls of Gurgaon or even at the flea markets. The most sellable fakes are Ed Hardy, Christian Audiger,CK, Armani and Reebok in New Delhi. So please watch what you are buying and from where you are buying! It's not only an investment in buying originals but it also boasts your confidence level. Surely you want it! Beleive you.